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United States Patent |
5,108,517
|
Kimura
,   et al.
|
April 28, 1992
|
Process for preparing titanium and titanium alloy materials having a
fine equiaxed microstructure
Abstract
According to the present invention, titanium and titanium alloy materials
having a fine equiaxed microstructure are produced. A titanium, .alpha.
titanium alloy or (.alpha.+.beta.) titanium alloy material is hydrogenated
in an amount of 0.02 to 2% by weight. If necessary, the hydrogenated
material is subjected to pretreatment [i.e., heated above 700.degree. C.
(.beta. transformation point)] and/or working (i.e., working at
450.degree. to 950.degree. C., or temperatures above .beta. transformation
point and below 1100.degree. C.). The material is then aged at 10.degree.
to 530.degree. C. or 10.degree. to 700.degree. C. (in the case of working
at temperatures above .beta. transformation point), and finally
dehydrogenated and recrystallized to prepared a material having a fine
equiaxed microstructure.
Inventors:
|
Kimura; Kinichi (Hikari, JP);
Hayashi; Masayuki (Hikari, JP);
Ishii; Mitsuo (Hikari, JP);
Yoshimura; Hirofumi (Hikari, JP);
Takamura; Jin-ichi (Kawasaki, JP)
|
Assignee:
|
Nippon Steel Corporation (Tokyo, JP)
|
Appl. No.:
|
558643 |
Filed:
|
July 26, 1990 |
Foreign Application Priority Data
| Jul 31, 1989[JP] | 1-198637 |
| Oct 16, 1989[JP] | 1-266310 |
| Dec 25, 1989[JP] | 1-336095 |
| Mar 06, 1990[JP] | 2-54592 |
Current U.S. Class: |
148/669; 148/527 |
Intern'l Class: |
C22C 014/00; C22C 001/00 |
Field of Search: |
148/11.5 F,12.7 B,133,11.5 R
|
References Cited
U.S. Patent Documents
2892742 | Jun., 1959 | Zwicker et al. | 148/11.
|
4415375 | Nov., 1983 | Lederich et al. | 148/11.
|
4820360 | Apr., 1989 | Eylon et al. | 148/133.
|
4822432 | Apr., 1989 | Eylon et al. | 148/127.
|
4832760 | May., 1989 | Eylon et al. | 148/20.
|
4871400 | Oct., 1989 | Shindo et al. | 148/11.
|
4889170 | Dec., 1989 | Mae et al. | 148/12.
|
4923513 | May., 1990 | Ducheyne et al. | 75/245.
|
Foreign Patent Documents |
63-4908A | Mar., 1986 | JP.
| |
63-4914A | Nov., 1986 | JP.
| |
1096359 | Apr., 1989 | JP | 148/11.
|
2025553 | Jan., 1990 | JP | 148/11.
|
Other References
W. R. Kerr et al. "Hydrogen as an alloying element in titanium (Hydrovac)"
Titanium '80 pp. 2477 2486.
N. C. Birla et al., "Anisatropy Control through the use of hydrogen in
Ti-6Al-4V alloy" Transaction of the india Institute of Metals, vol. 37,
No. 5, Oct. 1984, pp. 631-635.
W. R. Kerr, "The Effect of Hydrogen as a Temporary Alloying Element on the
Microstructure and Tensile Properties of Ti-6Al-4V" Metallurgical
Transactions A, vol. 16A, Jun. 1985 pp. 1077.about.1087.
Proceedings of Titanium '80 Conference, May 22, 1980, pp. 2477-2481, W.
Kerr et al.
|
Primary Examiner: Roy; Upendra
Attorney, Agent or Firm: Kenyon & Kenyon
Claims
We claim:
1. A process for preparing titanium and titanium alloy materials having a
fine equiaxed microstructure which comprises hydrogenating a titanium, a
.beta. titanium alloy or (.alpha.+.beta.) titanium alloy in an amount of
0.02 to 2.0% by weight of hydrogen, aging the hydrogenated material at
temperatures of 10.degree. to 530.degree. C. and dehydrogenating the
material in vacuum, and simultaneously, recrystallizing the material.
2. A process according to claim 1, wherein the hydrogenated titanium,
.alpha. titanium alloy or (.alpha.+.beta.) titanium alloy is pretreated in
such a manner that the material is heated at temperatures of 700.degree.
to 1100.degree. C. and cooled, and then subjected to said aging.
3. A process according to claim 1, wherein the hydrogenated titanium,
.alpha. titanium alloy or (.alpha.+.beta.) titanium alloy is worked at
temperatures of 450.degree. to 950.degree. C. in (.alpha.+.beta.) region
with a reduction of at least 30% and then subjected to said aging.
4. A process according to claim 1, wherein the hydrogenated titanium,
.alpha. titanium alloy or (.alpha.+.beta.) titanium alloy is heat-treated
in such a manner that the material is heated at temperatures above the
.beta. transformation point and cooled, worked at temperatures of
450.degree. to 950.degree. C. in (.alpha.+.beta.) region, and then
subjected to said aging.
5. A process according to claim 1, wherein the hydrogenated titanium,
.alpha. alloy or (.alpha.+.beta.) titanium alloy is worked in such a
manner that the material is worked at temperatures above the .beta.
transformation point and below 1100.degree. C. with a reduction of 30% of
more, which is finished in .beta. single phase region, and the aging is
then conducted at temperatures of 10.degree. to 530.degree. C.
6. A process according to claim 1, wherein the hydrogenated titanium,
.alpha. titanium alloy or (.alpha.+.beta.) titanium alloy is heat-treated
in such a manner that the material is heated above the .beta.
transformation point and below 1100.degree. C. and then cooled to
400.degree. C. or lower, worked in such a manner that the heat-treated
material is worked at temperatures above the .beta. transformation point
and below 1100.degree. C., which is finished in the .beta. single phase
region, and the aging is then conducted at temperatures of 10.degree. to
530.degree. C.
7. A process according to claim 1, wherein the material having an acicular
microstructure is hydrogenated in an amount of 0.02 to 2% by weight, aged
at temperatures of 10.degree. to 530.degree. C. and then annealed in
vacuum.
8. A process according to claim 2, wherein the material having an acicular
microstructure is hydrogenated in an amount of 0.02 to 2% by weight, aged
at temperatures of 10.degree. to 530.degree. C. and then annealed in
vacuum.
9. A process according to claim 3, wherein the working temperature of the
titanium is 450.degree. to 800.degree. C. in the (.alpha.+.beta.) region.
10. A process according to claim 3, wherein the working temperature of the
.alpha. titanium alloy is 600.degree. to 950.degree. C. in the
(.alpha.+.beta.) region.
11. A process according to claim 3, wherein the working temperature of the
(.alpha.+.beta.) titanium alloy is 550.degree. to 900.degree. C. in the
(.alpha.+.beta.) region.
12. A process according to claim 4, wherein the working temperature of the
titanium is 450.degree. to 800.degree. C. in the (.alpha.+.beta.) region.
13. A process according to claim 4, wherein the working temperature of the
.alpha. titanium alloy is 600.degree. to 950.degree. C. in the
(.alpha.+.beta.) region.
14. A process according to claim 4, wherein the working temperature of the
(.alpha.+.beta.) titanium alloy is 550.degree. to 900.degree. C. in the
(.alpha.+.beta.) region.
15. A process according to claim 7, wherein said acicular microstructure is
an acicular microstructure of a welded construction material comprising
said material.
16. A process according to claim 15, wherein said acicular microstructure
is an acicular microstructure of a welded construction material comprising
said material.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a process for preparing titanium and a
titanium alloy material having a superior fatigue strength and workability
particularly a process for preparing a titanium, .alpha. titanium alloy or
(.alpha.+.beta.) titanium alloy having a fine equiaxed microstructure.
(2) Description of the Related Art
Titanium and its alloys have been used in various material applications,
including aerospace materials, owing to their high strength-to-density
ratio and high corrosion resistance, and the applications thereof are
expanding. The reason why titanium and .alpha. and (.alpha.+.beta.)
titanium alloys are in such great demand is that they have a high strength
and ductility, but the characteristics requirements in each field are very
strict, and in particular, aerospace materials, etc., used under an
environment subject to cyclic stresses must have superior fatigue
properties, in addition to a good workability. This has led to
establishment of strict quality standards (e.g., as seen in AMS4967), and
to meet such requirements, the .alpha. grain of the material must have a
fine equiaxed microstructure.
Since the impurity contents of titanium are limited, an equiaxed
microstructure can be obtained by the conventional working and heat
treatment, but it has been difficult to homogeneously refine the
microstructure.
On the other hand, products used in the above-described field and having
various shapes (plate, wire, tube, rod, etc.) and made of .alpha. and
(.alpha.+.beta.) titanium alloys, are usually manufactured by a
combination of hot working and heat treatments. The step of the hot
working, however, has a drawback that a proper working temperature range
is too narrow to satisfy both of the following requirements; (1) ensuring
of a good workability for attaining a very precise product shape, (2) a
formation of an equiaxed microstructure in the product.
Further, in the above-described temperature range, the microstructure is
highly sensitive to temperature change; for example, even a slight rise in
the temperature causes grain growth, and thus the microstructure after
working tends to become heterogeneous. Further, the microstructure formed
during hot working does not undergo any significant change.
This has led to proposals for a process for preparing .alpha. and
(.alpha.+.beta.) titanium alloys having an equiaxed microstructure, e.g.,
a preparation process disclosed in Japanese Examined Patent Publication
No. 63-4914 wherein heating and working are repeated in a specific narrow
temperature range, and a preparation process disclosed in Japanese
Examined Patent Publication No. 63-4908, wherein a hot rolling material is
heated at temperatures above the .beta. transformation point.
Nevertheless, these processes cannot satisfactorily attain a homogeneously
fine equiaxed microstructure of a material. Further, the former is
disadvantageous in that the productivity is poor and the production cost
is high.
Techniques which utilize hydrogen as a temporary alloying element in
titanium alloys for improving their workability and microstructure are
disclosed in the following literature.
(1) U. Zwicker et al., U.S. Pat. No. 2,892,742 (issued on Jun. 30, 1959):
This patent describes that an .alpha. titanium alloy having an Al content
of 6% or more is hydrogenated in an amount of 0.05 to 1.0% by weight of
hydrogen, to improve the hot workability, and finally, dehydrogenated in
vacuum, but makes no mention of a refinement of the microstructure.
(2) W.R. Kerr et al., "Hydrogen as an alloying element in titanium
(Hydrovac)", Titanium ,80, P. 2477-2486:
This paper states that a hydrogenation of Ti-6Al-4V alloy as an
(.alpha.+.beta.) titanium alloy improves the hot workability through a
lowering of the .beta. transformation point, and provides a fine
microstructure. The hot working is conducted by forging at a reduction of
60% or less, and the forging is conducted in a slow speed ram motion
system at a ram speed of 1.27 .times.10.sup.-3 or less. Namely, this
working is not a practical working such that a strong working can be
conducted by hot rolling, etc.
(3) N. C. Birla et al., "Anisotropy control through the use of hydrogen in
Ti-6Al-4V alloy", Transactions of the Indian Institute of Metals, Vol. 37,
No. 5, Oct. 1984, P. 631-635:
This paper states that a hydrogenation of Ti-6Al-4V alloy as an
(.alpha.+.beta.) titanium alloy followed by hot rolling improves the
anisotropy of tensile properties. In this process, however, a hydrogenated
plate is homogenized at 990.degree. C. for 2 hrs, and a 50% rolling at
730.degree. C. is conducted in several passes of a 10% reduction of each
pass with a homogenization treatment of 10 minutes after each reduction,
which renders this process unsuitable for practical use.
(4) D. Eylon et al., U.S. Pat. No. 4,820,360 (Apr. 11, 1989):
This patent discloses a method of refining the microstructure of cast
titanium alloy articles, which method comprises heating a cast article at
780.degree. to 1020.degree. C. in a hydrogen-containing atmosphere to
hydrogenate the cast article, cooling the hydrogenated cast article to
room temperature at a controlled rate of 5.degree. to 40.degree. C./min,
and heating the cooled hydrogenated cast article in vacuum at 650.degree.
to 750.degree. C. for dehydrogenation.
(5) D. Eylon et al., U.S. Pat. No. 4,832,760 (May 23, 1989):
This patent discloses a method of refining the microstructure of prealloyed
titanium alloy powder compacts, which method comprises heating a compacted
article in a hydrogen-containing atmosphere at 780.degree. to 1020.degree.
C. for hydrogenation, cooling the hydrogenated compacted article to room
temperature at a rate of 5.degree. to 40.degree. C., and heating the
cooled hydrogenated compacted article in vacuum at 650.degree. to
750.degree. C. for dehydrogenation.
(6) W. R. Kerr, "The Effect of Hydrogen as a Temporary Alloying Element on
the Microstructure and Tensile Properties of Ti-6Al-4V", METALLURGICAL
TRANSACTIONS A, Vol. 16A, June 1985, P. 1077-1087:
The method disclosed in this paper comprises hydrogenating Ti-6Al-4V alloy
as an (.alpha.+.beta.) titanium alloy, heating the hydrogenated alloy at
870.degree. C., subjecting the heated alloy to eutectoid transformation at
540.degree. to 700.degree. C., and dehydrogenating the transformed alloy
at 650.degree. to 760.degree. C. to obtain a fine equiaxed microstructure.
Nevertheless, the above-described prior arts do not provide a sufficiently
fine equiaxed microstructure, i.e., are unsatisfactory when attempting to
stably prepare titanium and titanium alloys having a high strength,
fatigue properties, and workability, etc., on a commercial scale.
SUMMARY OF THE INVENTION
An object of the present invention is to form a fine and equiaxial
microstructure of titanium, .alpha. titanium alloys and (.alpha.+.beta.)
titanium alloys to an extent unattainable in the prior arts, and to
provide a process for stably preparing the above-described materials
having a high strength, fatigue properties, and workability, etc., on a
commercial scale.
To attain the above-described object, the present invention has the
following constitution.
Specifically, the present invention relates to a process for preparing
titanium and .alpha. and (.alpha.+.beta.) titanium alloys, characterized
by comprising aging, at temperatures of 10.degree. to 530.degree. C., a
material hydrogenated in an amount of 0.02 to 2.0% by weight of hydrogen,
and then dehydrogenating in vacuum, and simultaneously, recrystallizing
the material. In this case, prior to the aging, the hydrogenated material
may be subjected to a pretreatment such that it is heated at 700.degree.
C. or higher and then cooled. Further, the present invention provides a
process which comprises, working the above-described hydrogenated material
in the (.alpha.+.beta.) region at 450.degree. to 950.degree. C. with a
reduction of 30% or more, aging the material, and dehydrogenating and
recrystallizing the aged material. Further, the present invention includes
a process which comprises, subjecting the above-described hydrogenated
material to a heat treatment, i.e., heating the material at temperatures
above the .beta. transformation point, and cooling the heated material,
and then conducting the above-described working, aging, and annealing in
vacuum. The working temperatures for titanium, .alpha. titanium alloys and
(.alpha.+.beta.) titanium alloys are preferably 450.degree. to 800.degree.
C., 600.degree. to 950.degree. C., and 550.degree. to 900.degree. C.,
respectively. Further, the present invention provides a process which
comprises working the hydrogenated material at temperatures above the
.beta. transformation point and below 1100.degree. C., with a reduction of
30% or more, finishing the working in a .beta. single phase region, aging
the worked material at temperatures of 10.degree. to 700.degree. C., and
then annealing the aged material in vacuum. In this case, the
above-described process may include a step of a heat treatment, which
comprises heating the above-described hydrogenated material at
temperatures above the .beta. transformation point and below 1100.degree.
C. and then cooling the heated material to 400.degree. C. or lower.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 7 are microphotographs (.times.500), wherein FIGS. 1 to 5
correspond to examples of the present invention and FIGS. 6 and 7
correspond to comparative examples.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention enables the microstructure of titanium and .alpha.
and (.alpha.+.beta.) titanium alloys to be rendered fine and equiaxed
without the conventional working and heat treatment, and provides a
material having superior fatigue properties and workability.
To solve the above-described problems of the prior arts, the present
inventors considered hydrogen, which can be easily incorporated in
titanium and removed therefrom, and conducted various studies to that end,
and as a result, found the following facts.
(a) When titanium and .alpha. and (.alpha.+.beta.) titanium alloys are
hydrogenated and then aged at relatively low temperatures, titanium
hydrides finely precipitate in the material and high density dislocations
are introduced in the interior of hydrides and their surrounding regions
as well. For the precipitation, the better results can be obtained when
the hydrogen content is higher and the aging is conducted under lower
temperatures and longer times. This causes the hydride to dispersively
precipitate in a larger amount as well as in a finer state, so that the
dislocation density described above becomes high. When this material is
heated in vacuum, it is dehydrogenated and simultaneously a number of
recrystallization nuclei are formed from the dense dislocation field, thus
resulting in the formation of a fine equiaxed microstructure.
(b) When the material is heated at proper temperatures in the
(.alpha.+.beta.) two phase region or the .beta. single phase region and
then cooled, hydrogen is more homogeneously dissolved during heating,
which results in a formation of a fine acicular martensitic microstructure
from the stabilized and increased .beta. phase during cooling. This causes
the hydride to more homogeneously and finely precipitate and, at the same
time, high density dislocations to be introduced in the interior of
hydrides and their surrounding regions in subsequent aging, so that a more
homogeneous and finer recrystallization microstructure can be obtained
after final annealing in vacuum.
(c) When titanium and .alpha. and (.alpha.+.beta.) titanium alloys are
hydrogenated, hydrogen is dissolved, so that the proportion of the .beta.
phase having an excellent workability becomes high even in a relatively
low temperature region.
Therefore, if necessary, after a .beta. heat treatment is conducted,
wherein the material is heated above the .beta. transformation point and
then cooled, the hot working can be conducted in an (.alpha.+.beta.)
region at temperatures below those used in the prior arts. This prevents
the grain growth during working at relatively high temperatures in the
prior arts, and further, during such working, a strain is accumulated and
a hydride precipitated, so that high density dislocations are introduced
into the material. During the subsequent aging, the hydride further
precipitates to enhance the dislocation density. This enables more fine
and equiaxed microstructure to be obtained during recrystallization in the
subsequent annealing in vacuum.
(d) When titanium and .alpha. and (.alpha.+.beta.) titanium alloys are
hydrogenated, hydrogen is dissolved in the material to lower the .beta.
transformation point. This enables the working in a .beta. region having
an excellent workability to be conducted at temperatures below those used
in the prior arts. As a result, coarsening of .beta. grains can be
prevented during hot working in the .beta. region, and a fine acicular
martensitic microstructure is formed during cooling after the completion
of the working in the .beta. region. This causes a fine hydride to
precipitate during the subsequent aging, so that grains in the
microstructure are refined.
The present invention will now be described in more detail.
The present inventors have conducted various experiments on the hydrogen
content, heating temperature, working temperature, reduction, and aging
temperature necessary for a refinement of grains in the microstructure,
and thus completed the present invention.
Examples of the object material of the present invention include
commercially available pure titanium such as titanium specified in JIS
(Japanese Industrial Standards), .alpha. titanium alloys such as
Ti-5Al-2.5Sn, and (.alpha.+.beta.) titanium alloys such as Ti-6Al-4V.
Casting materials such as ingot, hot working materials subjected to
blooming, hot rolling, hot extrusion, etc., or cold working materials, and
further powder compacts, etc., may be used as the material. The reason for
the limitation of the hydrogen content is as follows. When the hydrogen
content is less than 0.02% by weight, the amount of the hydride
precipitated during aging is too small to form the intended fine equiaxed
microstructure in the subsequent annealing. On the other hand, when the
hydrogen content exceeds 2% by weight, the hydride precipitates in a large
amount during aging. In this stage, however, the material per se becomes
very brittle, which brings about problems in the handling of the material
such as that it becomes impossible to conduct subsequent annealing in
vacuum. Therefore, the hydrogen content is limited to 0.02 to 2% by
weight. The hydrogenation method depends upon the hydrogenation during
melting, heat treatment in a hydrogen atmosphere, etc., but there is no
particular limitation on the hydrogenation methods and conditions.
The aging of the above-described material will now be described.
When the aging temperature is below 10.degree. C., the hydride is finely
precipitated, but a very long time is needed for the precipitation, which
renders these temperatures impractical from the view point of industry. On
the other hand, when the aging temperature exceeds 530.degree. C.,
although precipitated in a large amount, the hydride is coarsened.
Further, when the temperature is too high, the hydride unfavorably
redissolves, which makes it impossible to form the intended fine equiaxed
microstructure in subsequent annealing. Therefore, the aging temperature
is limited to 10.degree. to 530.degree. C. Although there is no particular
limitation on the holding time, it should be 1 min to 50 hr (holding for a
short time in the case of a high temperature and holding for a long time
in the case of a low temperature). Specific examples of the method of
aging include one wherein the material is heated from room temperature to
the aging temperature and held at that temperature, one wherein the
material is held at a room temperature of 10.degree. C. or higher, and one
wherein the material is cooled from the hydrogenating temperature,
pretreatment temperature or working temperature to the aging temperature
and then held at that temperature.
After the above-described aging, annealing is conducted in vacuum, as a
final step, to dehydrogenate and simultaneously recrystallize the
material. There is no particular limitation on the annealing conditions,
and the annealing may be conducted under conditions commonly used for
recrystallization after working, but preferably, the annealing temperature
is as low as possible. Specifically, the annealing temperature and time
are preferably 500.degree. to 900.degree. C. and 100 hr or less,
respectively. A remaining of hydrogen in a certain amount or more becomes
a cause of embrittlement and deteriorates the product characteristics. The
degree of vacuum may be a reduced pressure of about 1 .times.10.sup.-1
Torr or less. The higher the degree of vacuum, the shorter the annealing
time. It is preferred from the practical point of view that the reduced
pressure be about 1.times.10.sup.-4 Torr and the residual gas be an inert
gas such as argon.
Pretreatments optionally conducted prior to the above-described aging will
now be described.
As described above, pretreatments prior to the aging make the
microstructure formed by the final vacuum annealing more homogeneous and
fiber. When the temperature for the pretreatment is below 700.degree. C.,
the amount of the .beta. phase is small and the effect of a formation of
the above-described martensitic microstructure on refining the
microstructure becomes poor. Therefore, the temperature for the
pretreatment is limited to 700.degree. C. or higher. When the temperature
is 700.degree. C. or higher, the amount of the .beta. phase increases and
the .beta. single phase region is formed depending upon the hydrogen
content, so that a finer microstructure as described above is obtained.
There is no particular limitation on the upper limit of the pretreatment
temperature, but preferably the upper limit is about 1100.degree. C., from
the viewpoint of surface oxidation and operations such as the performance
of heat treating furnace. Although there is no particular limitation on
the holding time, at least 1 min is necessary. With respect to cooling
after holding, any of furnace cooling, air cooling, and water quenching
may be applied, but a higher cooling rate is preferred. The finishing
temperature of cooling is preferably 530.degree. C. or lower.
The above-described process of the present invention may be applied to
materials having an acicular microstructure such as the above-described
commercially available pure titanium, .alpha. titanium alloys and
(.alpha.+.beta.) titanium alloys or the above-described welded materials,
brazed materials and welded pipe products.
Specifically, the above-described materials and products having a coarse
acicular microstructure are hydrogenated in an amount of 0.02 to 2% by
weight of hydrogen. If necessary, the hydrogenated materials are subjected
to a pretreatment such that they are heated at a temperature of
700.degree. C. or higher and then cooled. The pretreated materials are
aged at temperatures of 10 to 530.degree. C. and then vacuum-annealed to
dehydrogenate and, at the same time, to recrystallize the materials,
thereby forming a fine equiaxed microstructure to improve the fatigue
properties and workability, etc.
Hydrogenation can be conducted by heat-treating the material in a hydrogen
atmosphere. For a welding construction material, the material may be
welded in an atmosphere comprising a mixture of an inert gas such as argon
with hydrogen, or the material may be hydrogenated prior to welding and
then welded.
Wording in the (.alpha.+.beta.) region optionally conducted prior to the
aging will now be described.
In the present invention, the working is conducted by rolling, extrusion,
and forging, etc. As described above, hydrogenation of a material
facilitates working in the (.alpha.+.beta.) region at low temperatures.
The higher the hydrogen content, the greater the above-described tendency.
But there is the temperature range appropriate for working in the
(.alpha.+.beta.) region on the low temperature side. Specifically, when
the temperature is below 450.degree. C., cracking occurs during working.
On the other hand, when the temperature is above 950.degree. C., a .beta.
region is formed depending upon the material or the hydrogen content.
Therefore, the working temperature is limited to 450.degree. to
950.degree. C.
The object materials, i.e., titanium, (.alpha.+.beta.) titanium alloys and
.alpha. titanium alloys, are slightly different from each other in the
workability, and the workability is slightly poorer in the order of
titanium, (.alpha.+.beta.) alloys and .alpha. titanium alloys, and the
.beta. transformation point becomes high in that order. Therefore, it is
preferred that titanium, (.alpha.+.beta.) titanium alloys and .alpha.
titanium alloys be worked in each (.alpha.+.beta.) region at 450.degree.
to 800.degree. C. being low temperatures, 550.degree. to 900.degree. C.
and 600.degree. to 950.degree. C. being high temperatures, respectively.
The reduction in the above-described working temperature region varies,
depending upon whether or not the .beta. heat treatment is conducted prior
to working. In the process wherein no .beta. heat treatment is conducted
[in the case of claim (3)], working with a reduction of 30% or more
enables fine equiaxed recrystallized grains to be formed by
recrystallization annealing after aging.
In the process wherein the .beta. heat treatment is previously conducted
[in the case of claim (4)], the above-described limitation of the
reduction is unnecessary. Specifically, when a hydrogenated material is
heated at temperatures above the .beta. transformation point and then
cooled, the material per se also becomes a fine microstructure. Therefore,
even when the reduction in the working of such a material is less than
30%, it is possible to prepare fine recrystallized grains through
subsequent aging and annealing in vacuum. The effect is significant when
the reduction is 15% or more.
The term "reduction" used therein is intended to mean a total reduction of
one or more workings.
In the .beta. transformation, the material is heated above the .beta.
transformation point and then cooled for the purpose of forming a fine
microstructure. In this case, the heating temperature is preferably as low
as possible. The holding time is preferably 1 to 60 min. The cooling may
be conducted by any of furnace cooling, air cooling and water quenching,
but the higher the cooling rate, the better the results. When the
finishing temperature of cooling is about 300.degree. C. below the .beta.
transformation point, a fine microstructure can be obtained. After the
material is heated above the .beta. transformation point, it is worked by
a method wherein the material is worked in the above-described working
temperature range in the course of cooling, a method which comprises
re-heating the material in the course of cooling or re-heating the
material cooled to room temperature and then working the re-heated
material in the above-described working temperature range, or a method
which comprises holding the material in the course of cooling at a certain
temperature in a heat temperature range and conducting the working at that
temperature.
There is no particular limitation on the upper limit of the above-described
reduction, and the reduction may be in a usually workable range. Further,
there is no particular limitation on the working time. After the working,
the aging is conducted after cooling to room temperature or in the course
of cooling. In this case, there is no particular limitation on the cooling
rate, but the higher the cooling rate, the better the results. After the
aging, as described above, the aged material is annealed in vacuum.
Working in the .beta. region, optionally conducted prior to the
above-described aging, will now be described.
In this case, the .beta. transformation point is lowered by hydrogenation
to conduct working at a temperature in the .beta. single phase region
having an excellent workability.
Specifically, the working is conducted at temperatures above the .beta.
transformation point and finished in the .beta. region. When the
temperature raised above the .beta. transformation point is too high, the
.beta. grains are coarsened, which makes it difficult to obtain a fine
equiaxed microstructure as a final intended product. For this reason, the
heating temperature is limited to less than 1100.degree. C. As described
above, the working is finished in the .beta. region for forming a fine and
acicular martensitic microstructure during cooling.
In the process described in claim 8, the hydrogenated material is heated at
temperatures above the .beta. transformation point, as described above to
conduct working. In this case, in consideration of including of coarse
grains in the microstructure of the material, the reduction is limited to
30% or more to refine the coarse grains.
In the process described in claim 9, the hydrogenated material is
pretreated, i.e., heated above the .beta. transformation point and cooled
to 400.degree. C. or below, and again heated above the .beta.
transformation point to conduct working. In this case, the .beta. heat
treatment as the pretreatment is conducted in consideration of including
of coarse grains in the microstructure of the material. Since the
microstructure is refined by this treatment, the reduction in the
above-described working may be 30% or less, but the effect is significant
when the reduction is 15% or more.
The term "reduction" used herein is intended to mean a total reduction in
one or more workings.
In the present invention, the cooling in the .beta. heat treatment as the
pretreatment may be conducted by any of furnace cooling, air cooling and
water quenching, but the higher the cooling rate, the better the result,
for the fine microstructure.
After the above-described working, the material is applied to the
above-described aging and annealing in vacuum. In this case, as opposed to
the working in the (.alpha.+.beta.) region, the upper limit of the aging
temperature can be increased to 700.degree. C., which makes it possible to
shorten the aging time, but a more significant effect on microstructure
refining can be attained when the aging temperature is 530.degree. C. or
lower.
In the above-described present invention, if a slight heterogeneous portion
occurs in the microstructure of the material after annealing in vacuum due
to the remaining of a coarse .alpha. phase around the former .beta. grain
boundary, one or two additional cold working-annealing procedures can be
conducted to homogenize the microstructure.
Further, in the present invention, a series of treatments of the present
invention can be repeated twice or more. In this case, a finer equiaxed
microstructure can be obtained.
As described above, each process of the present invention enables titanium
and titanium alloy materials having a fine equiaxed microstructure to be
stably prepared on a commercial scale, so that the above-described
materials having an excellent strength, fatigue properties, and
workability, etc. can be stably supplied.
EXAMPLE
EXAMPLE 1
Results of experiment conducted by using a plate (thickness: 4 mm) of a
Ti-6Al-4V as a representative (.alpha.+.beta.) alloy without conducting a
pretreatment of aging with various changes of the hydrogen content and
aging conditions will now be described. All of the materials were annealed
in vacuum at 700.degree. C. for 5 hrs for dehydrogenation and
recrystallization.
The experimental conditions and evaluation results of microstructure of the
finally prepared materials are shown in Table 1. Material No. 25 having a
hydrogen content of 2.2% by weight became very brittle and cracked during
aging, so that subsequent annealing in vacuum could not be conducted. FIG.
1 is a micrograph of an example of the present invention (No. 14 shown in
Table 1) wherein a material having a hydrogen content of 0.9% by weight as
a representative example of the microstructure was aged at 500.degree. C.
for 8 hrs and then annealed in vacuum at 700.degree. C. for 5 hrs, thereby
dehydrogenating the material. FIG. 6 is a micrograph of a comparative
material prepared by repeatedly heating and hot rolling without addition
of hydrogen and then annealing the treated material for recrystallization.
Thus, it is apparent that according to the present invention, a material
having a fine equiaxed microstructure can be obtained.
The same experiment as that described above was conducted on titanium (JIS
grade 2) and Ti-5Al-2.5Sn alloy, except that with respect to titanium,
annealing in vacuum as a final step was conducted by holding the material
at 600.degree. C. for 1 hr. The experimental conditions and results are
shown in Tables 2 and 3. From the results, it is apparent that the same
effect as that of the above described experiment can be attained.
TABLE 1
______________________________________
Experimental results of Ti--6Al--4V alloy
Evaluation
results of
Experimental conditions
microstructure
Hydrogen Aging Aging Grain
Classi- Run content by
temp. time size Aspect
fication
No. weight (%)
(.degree.)
(hr) (.mu.m)
ratio
______________________________________
Present 1 0.02 500 20 6 1.1
invention
2 0.04 500 10 5 1.0
3 0.2 300 15 3 1.1
4 0.2 400 8 3 1.1
5 0.2 500 3 4 1.0
6 0.9 20 40 3 1.1
7 0.9 50 30 3 1.1
8 0.9 100 20 2 1.1
9 0.9 300 8 2 1.0
10 0.9 400 5 2 1.0
11 0.9 500 0.1 5 1.1
12 0.9 500 0.5 4 1.1
13 0.9 500 2 3 1.0
14 0.9 500 8 2 1.0
15 1.0 400 3 2 1.0
16 1.0 500 0.5 3.7 1.1
17 1.0 500 2 2.8 1.0
18 1.0 500 8 1.8 1.0
19 1.5 400 3 2 1.0
20 1.5 500 1 3 1.0
21 2.0 100 15 2 1.0
Compar- 22 0.01 500 20 12 1.4
ative 23 0.9 0 50 10 1.4
24 0.9 550 8 13 1.2
25 2.2 100 15 -- --
______________________________________
TABLE 2
______________________________________
Experimental results of titanium (JIS grade 2)
Evaluation
results of
Experimental conditions
microstructure
Hydrogen Aging Aging Grain
Classi- Run content by
temp. time size Aspect
fication
No. weight (%)
(.degree.)
(hr) (.mu.m)
ratio
______________________________________
Present 1 0.02 400 15 8 1.1
invention
2 0.2 250 8 7 1.0
3 0.2 400 5 8 1.0
4 0.5 20 40 9 1.1
5 0.5 100 10 6 1.1
6 0.5 200 8 5 1.1
7 0.5 400 2 6 1.0
Compar- 8 0.01 400 15 19 1.1
ative 9 0.5 0 50 15 1.1
10 0.5 550 2 20 1.0
______________________________________
TABLE 3
______________________________________
Experimental results of Ti--5Al--2.5Sn
Evaluation
results of
Experimental conditions
microstructure
Hydrogen Aging Aging Grain
Classi- Run content by
temp. time size Aspect
fication
No. weight (%)
(.degree.)
(hr) (.mu.m)
ratio
______________________________________
Present 1 0.02 500 20 7 1.1
invention
2 0.2 500 3 5 1.0
3 0.9 300 8 3 1.1
4 0.9 500 2 4 1.0
5 1.0 300 6 3 1.0
6 1.0 500 1 4 1.0
Compar- 7 0.01 500 20 14 1.3
ative 8 0.9 0 50 12 1.5
9 0.9 550 2 15 1.2
______________________________________
EXAMPLE 2
The results of experiments conducted by using a plate (thickness: 4 mm) of
a Ti-6Al-4V as a representative (.alpha.+.beta.) titanium alloy with
various changes of pretreatment temperature in addition to the hydrogen
content and aging condition will now be described. All of the materials
were annealed in vacuum at 700.degree. C. for 5 hrs for dehydrogenation
and recrystallization.
The experimental conditions and evaluation results of microstructure of
finally prepared materials are shown in Table 4. A material (No. 24 shown
in Table 4) having a hydrogen content of 2.2% by weight became very
brittle and cracked during aging, so that subsequent annealing in vacuum
could not be conducted. FIG. 2 is a micrograph of an example of the
present invention (No. 16 shown in Table 4) wherein a material having a
hydrogen content of 1.0% by weight as a representative example of the
microstructure was pretreated at 830.degree. C., aged at 500.degree. C.
for 8 hrs, and annealed in vacuum at 700.degree. C. for 5 hrs for
dehydrogenation and recrystallization. FIG. 6 is a micrograph of a
comparative material prepared by repeatedly heating and hot rolling
without hydrogenation and then annealing the treated material for
recrystallization. Thus, it is apparent that, according to the present
invention, it is possible to obtain a material having a fine equiaxed
microstructure.
The same experiment as that described above was conducted on titanium (JIS
grade 2) and Ti-5Al-2.5Sn alloy as a representative .alpha. titanium alloy
except that, with respect to titanium, annealing in vacuum as a final step
was conducted by holding the material at 600.degree. C. for 1 hr. The
experimental conditions and results are shown in Tables 5 and 6. From the
results, it is apparent that the same effect as that of the
above-described experiments can be attained.
TABLE 4
__________________________________________________________________________
Experimental results of Ti--6Al--4V alloy
(Pretreatment effected)
Evaluation results
Experimental conditions of microstructure
Hydrogen content,
Pretreatment
Aging Aging
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
temp. (.degree.C.)
time (hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.02 1050 500 10 4 1.0
invention
2 0.2 900 300 15 2 1.1
3 0.2 900 400 8 2 1.1
4 0.2 1000 500 3 3 1.0
5 1.0 850 20 40 2 1.1
6 1.0 850 50 30 2 1.0
7 1.0 950 100 20 1.5 1.1
8 1.0 700 300 8 1.5 1.0
9 1.0 830 400 3 1.5 1.0
10 1.0 750 500 0.1 4 1.1
11 1.0 800 500 0.5 3 1.0
12 1.0 950 500 0.5 2.5 1.0
13 1.0 750 500 2 2.5 1.0
14 1.0 830 500 2 2 1.0
15 1.0 750 500 8 1.5 1.0
16 1.0 830 500 8 1 1.0
17 1.5 850 400 3 1.5 1.0
18 1.5 850 500 1 2 1.0
19 2.0 850 100 15 1.5 1.0
Comparative
20 0.01 750 500 10 12 1.3
21 1.0 650 550 8 10 1.2
22 1.0 850 0 50 9 1.4
23 1.0 750 550 8 12 1.2
24 2.2 850 100 15 -- --
__________________________________________________________________________
TABLE 5
__________________________________________________________________________
Experimental results of Titanium JIS grade 2
(Pretreatment effected)
Evaluation results
Experimental conditions of microstructure
Hydrogen content,
Pretreatment
Aging Aging
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
temp. (.degree.C.)
time (hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.02 900 250 10 8 1.1
invention
2 0.2 800 250 8 6 1.0
3 0.5 750 20 40 7 1.0
4 0.5 750 100 10 5 1.0
5 0.5 750 200 8 4 1.0
6 0.5 750 400 2 5 1.0
Comparative
7 0.01 900 250 10 16 1.1
8 0.5 750 0 50 13 1.1
9 0.5 750 550 2 18 1.0
__________________________________________________________________________
TABLE 6
__________________________________________________________________________
Experimental results of Ti--5Al--2.5Sn alloy
(Pretreatment effected)
Evaluation results
Experimental conditions of microstructure
Hydrogen content,
Pretreatment
Aging Aging
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
temp. (.degree.C.)
time (hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.02 1100 500 20 6 1.1
invention
2 0.2 1000 500 3 4 1.0
3 1.0 750 300 6 2.5 1.0
4 1.0 850 500 1 3 1.0
Comparative
5 0.01 1100 500 20 12 1.4
6 1.0 650 500 2 12 1.4
7 1.0 850 0 50 10 1.5
8 1.0 850 550 2 13 1.2
__________________________________________________________________________
EXAMPLE 3
Slabs of Ti-6Al-4V alloy as a representative (.alpha.+.beta.) titanium
alloy subjected to hydrogenation so as to respectively have hydrogen
contents of 0.01%, 0.05%, 0.2%, 0.5%, 0.9%, 1.5% and 2.2% by weight were
each heated at 500.degree. C., 600.degree. C., 700.degree. C. and
800.degree. C. and then hot rolled with reductions of 30%, 60%, 70% and
80%. After the hot rolling, the materials were cooled to room temperature,
heated at 500.degree. C., held for 8 hrs at that temperature for aging,
and then heated at 700.degree. C. for 1 hr under a vacuum of
1.times.10.sup.-4 Torr for dehydrogenation and recrystallization.
The evaluation results of microstructure of the materials which have been
hot rolled, aged and annealed in vacuum are shown in tables 7 to 12.
Materials which have been hydrogenated to have hydrogen contents of 0.05%,
0.2%, 0.5%, 0.9% and 1.5% by weight, hot-rolled at 600.degree. C.,
700.degree. C. and 800.degree. C. with a reduction of 30% or more had a
fine equiaxed microstructure. FIG. 3 is a micrograph of a representative
example wherein a material having a hydrogen content of 0.2% by weight was
hot-rolled at 750.degree. C. with a reduction of 80%. The material having
a hydrogen content of 2.2% by weight became very brittle when hot-rolled
and then cooled to room temperature, which made it impossible to conduct
subsequent treatments.
FIG. 7 is a micrograph of a comparative material prepared by the
conventional process, i.e., by hot-rolling Ti-6Al-4V alloy free from
hydrogen at 950.degree. C. with a reduction of 80% and then
recrystallizing the material.
Compared to the materials prepared by the conventional process, the
materials prepared according to the present invention had a finer equiaxed
microstructure and superior fatigue strength and workability.
TABLE 7
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
0.01% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .DELTA.
.DELTA. .DELTA.
.DELTA.
700 .DELTA.
.DELTA. .DELTA.
.DELTA.
800 .DELTA.
.DELTA. .DELTA.
.DELTA.
______________________________________
Note:
.DELTA.: Partially fine equiaxed microstructure.
TABLE 8
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
0.05% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
TABLE 9
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
0.2% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
TABLE 10
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
0.5% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
TABLE 11
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
0.9% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
TABLE 12
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (Hydrogen content:
1.5% by weight)
Hot rolling Reduction (%)
temp. (.degree.C.)
30 60 70 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
EXAMPLE 4
Hydrogenated Ti-6Al-4V alloy [(.alpha.+.beta.) type] slabs having a
hydrogen content of 0.2% by weight were subjected to .beta. heat
treatment, i.e., heated at 850.degree. C. and 950.degree. C. being
temperatures above the .beta. transformation point in the above-described
hydrogen content, and air-cooled to room temperature, and then hot-rolled
at 500.degree. C., 600.degree. C., 700.degree. C., 750.degree. C. and
800.degree. C. with reductions of 22%, 40%, 60% and 80%. After the hot
rolling, the materials were cooled to room temperature, heated at
500.degree. C., held for 8 hrs at that temperature for aging, and heated
at 700.degree. C. for 1 hr under a vacuum of 1 .times.10.sup.-4 Torr for
dehydrogenation and recrystallization. The Evaluation results of
microstructure of the above-described materials are shown in Table 13 and
14. All of the materials which have been hot-rolled at 600 .degree. C.,
700.degree. C., 750.degree. C. and 800.degree. C. had a fine equiaxed
microstructure in all of the reductions.
TABLE 13
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (.beta. heat treatment
at 850.degree. C. effected)
Hot rolling Reduction (%)
temp. (.degree.C.)
22 40 60 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
750 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
TABLE 14
______________________________________
Evaluation results of microstructure of the
dehydrogenated materials (.beta. heat treatment
at 950.degree. C. effected)
Hot rolling Reduction (%)
temp. (.degree.C.)
22 40 60 80
______________________________________
500 .DELTA.
.DELTA. .DELTA.
.DELTA.
600 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
700 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
750 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
800 .smallcircle.
.smallcircle.
.smallcircle.
.smallcircle.
______________________________________
Note:
.smallcircle.: Completely fine equiaxed microstructure.
.DELTA.: Partially fine equiaxed microstructure.
EXAMPLE 5
(1) Hydrogenated Ti-6Al-4V alloy [(.alpha.+.beta.) type] slabs having
varied hydrogen contents were subjected to the .beta. heat treatment,
i.e., heated at temperatures above the .beta. transformation point
corresponding to the above-described hydrogen content and air-cooled to
room temperature. The heat-treated materials and the above-described
materials not subjected to the .beta. heat treatment were hot-rolled at
750.degree. C. with a reduction of 60% to prepare 4 mm thick plates. Then,
the plates were aged under various conditions and heated at 730.degree. C.
for 5 hrs under a vacuum of 1 .times.10.sup.-4 Torr for dehydrogenation
and recrystallization. The grain size and aspect ratio of the final
materials are shown in Table 15 together with the .beta. heat treatment
temperature and aging conditions. FIG. 4 is a micrograph of the material
No. 16 of the present invention shown in Table 15. A material having a
hydrogen content of 2.2% by weight as well hot-rolled under the
above-described conditions, but this material became very brittle after
cooling, which made it impossible to conduct subsequent treatments.
It is apparent that, according to the present invention, an
(.alpha.+.beta.) titanium alloy having a fine equiaxed microstructure can
be obtained.
(2) JIS grade 2 titanium was subjected to treatments for the aging in the
same manner as described in the above item (1), and then annealed at
630.degree. C. for 5 hrs under a vacuum of 1.times.10.sup.-4 Torr for
dehydrogenation and recrystallization. The results are shown in Table 16.
As apparent from the results, according to the present invention, titanium
having a fine equiaxed microstructure can be obtained.
(3) Ti-5Al-2.5Sn alloy as a representative .alpha. titanium alloy was
subjected to treatments to the final treatment in the same manner as that
described in the above item (1). The results are shown in Table 17. As
apparent from the results, according to the present invention, an .alpha.
titanium alloy having a fine equiaxed microstructure can be obtained.
TABLE 15
__________________________________________________________________________
Experimental results of Ti--6Al--4V alloy
Aging
.beta. heat
conditions
Hydrogen content
treatment
Temp.
Time
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
(.degree.C.)
(hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.03 -- 500 10 6 1.1
invention
2 0.03 1000 500 10 5 1.0
3 0.15 900 300 15 3 1.1
4 0.15 -- 400 8 5 1.1
5 0.15 900 400 8 4 1.0
6 0.15 900 500 3 5 1.0
7 0.4 860 20 40 <1 1.1
8 0.4 860 50 30 <1 1.0
9 0.4 860 100 20 1 1.1
10 0.4 860 300 8 2 1.0
11 0.4 860 400 5 3 1.0
12 0.4 -- 500 0.1 6 1.1
13 0.4 860 500 0.1 5 1.1
14 0.4 860 500 0.5 5 1.1
15 0.4 860 500 2 4 1.0
16 0.4 860 500 8 3 1.0
17 2.0 830 100 15 <1 1.0
Comparative
18 0.01 1040 500 15 11 1.4
19 0.4 -- 600 8 16 1.3
20 0.4 860 600 8 14 1.2
21 2.2 830 100 15 -- --
__________________________________________________________________________
TABLE 16
__________________________________________________________________________
Experimental results of Titanium JIS grade 2
Aging
.beta. heat
conditions
Hydrogen content
treatment
Temp.
Time
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
(.degree.C.)
(hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.15 -- 250 5 6 1.1
invention
2 0.15 880 250 5 5 1.0
3 0.2 -- 100 8 4 1.1
4 0.2 850 100 8 2 1.1
5 0.2 850 200 2 4 1.0
Comparative
6 0.01 950 250 10 15 1.4
7 0.3 -- 600 2 18 1.4
8 0.3 820 600 2 17 1.3
__________________________________________________________________________
TABLE 17
__________________________________________________________________________
Experimental results of Ti--5Al--2.5Sn alloy
Aging
.beta. heat
conditions
Hydrogen content
treatment
Temp.
Time
Grain
Aspect
Classification
Run No.
by weight (%)
temp. (.degree.C.)
(.degree.C.)
(hr)
size (.mu.m)
ratio
__________________________________________________________________________
Present
1 0.15 -- 500 3 6 1.1
invention
2 0.15 950 500 3 5 1.0
3 0.2 -- 300 8 3 1.1
4 0.2 930 300 8 2 1.1
5 0.2 930 500 2 4 1.0
Comparative
6 0.01 1080 500 15 12 1.4
7 0.5 -- 600 2 15 1.4
8 0.5 900 600 2 14 1.3
__________________________________________________________________________
EXAMPLE 6
(1) A Ti-6Al-4V alloy slab as an (.alpha.+.beta.) titanium alloy was heated
in a hydrogen atmosphere of 1 atmospheric pressure at 800.degree. C. for 1
to 40 hrs so as to have the hydrogen contents shown in Table 18 and
hot-rolled at temperatures shown in Table 18 with a reduction of 60% to
prepare 6 mm thick plates. After the hot rolling, the plates were cooled
to room temperature, held for 8 hrs at 500.degree. C. for aging, and
annealed in vacuum at 700.degree. C. for 10 hrs for dehydrogenation and
recrystallization. The microstructure of the central portion of each
material was observed, and as a result it was found that, as shown in
Table 18, the materials prepared by heating materials having hydrogen
contents of 0.25%, 1.6% and 2.1% by weight at 910.degree. C. and
1000.degree. C. in the .beta. region and hot-rolling and aging the
materials had an intended fine equiaxed microstructure.
A representative microstructure prepared by hot-rolling a material having a
hydrogen content of 0.25% by weight at 910.degree. C., aging the
hot-rolled material at 500.degree. C. for 8 hrs and annealing the aged
material in vacuum is shown in FIG. 5. The materials having a hydrogen
content as low as 0.006% provided no intended microstructure at any
temperature. The microstructure of the materials having hydrogen contents
of 0.25%, 1.6% and 2.1% by weight was refined to a certain extent by
hot-rolling at 1100.degree. C., but an intended microstructure cannot be
obtained from these materials because the original .beta. grain is coarse.
The material having a hydrogen content of 2.1% by weight cracked during
handing after aging.
TABLE 18
______________________________________
Hydrogen
content
by weight
Hot rolling temp. (.degree.C.)
(%) 910 1000 1100
______________________________________
0.006 Coarse Coarse Coarse
equiaxed acicular acicular
microstructure
microstructure
microstructure
0.25 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
1.6 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
2.1 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
______________________________________
(2) An ingot of Ti-6Al-4V alloy as an (.alpha.+.beta.) titanium alloy was
heated in a hydrogen atmosphere of 1 atmospheric pressure at 850.degree.
C. for 2 to 30s hr to prepare hydrogenated materials having hydrogen
contents shown in Table 19 and hot-extruded at 950.degree. C. with a
reduction of 80% to prepare round bars having a diameter of 40 mm. After
the hot-extrusion, the round bars were cooled to room temperature and then
held for 8 hrs at temperatures shown in Table 19 for aging. Thereafter,
the round bars were annealed in vacuum at 750.degree. C. for 15 hrs for
dehydrogenation and recrystallization. The microstructure of the central
portion of each material was observed. As shown in Table 19, the materials
having hydrogen contents of 0.21%, 1.3% and 2.2% by weight provided an
intended fine equiaxed microstructure when the aging temperature was
50.degree. C., 300.degree. C. and 500.degree. C. The material having a
hydrogen content as low as 0.007% by weight provided no intended
microstructure at any aging temperatures. The materials subjected to aging
at 0.degree. C. had an ununiform microstructure in any hydrogen content.
The materials subjected to aging at 800.degree. C. had a coarse equiaxed
microstructure in any hydrogen content. The material having a hydrogen
content of 2.2% by weight cracked during handling after aging.
TABLE 19
__________________________________________________________________________
Hydrogen content
Aging temperature (.degree.C.)
by weight (%)
0 50 300 500 800
__________________________________________________________________________
0.007 Not uniform equiaxed
Not uniform equiaxed
Not uniform equiaxed
Not uniform equiaxed
Coarse equiaxed
microstructure
microstructure
microstructure
microstructure
microstructure
0.21 Not uniform equiaxed
Fine equiaxed
Fine equiaxed
Fine equiaxed
Coarse equiaxed
microstructure
microstructure
microstructure
microstructure
microstructure
1.3 Not uniform equiaxed
Fine equiaxed
Fine equiaxed
Fine equiaxed
Coarse equiaxed
microstructure
microstructure
microstructure
microstructure
microstructure
2.2 Not uniform equiaxed
Fine equiaxed
Fine equiaxed
Fine equiaxed
Coarse equiaxed
microstructure
microstructure
microstructure
microstructure
microstructure
__________________________________________________________________________
The JIS grade 2 commercially pure titanium was also subjected to
treatments, to the aging, in the same manner as described in the above
item (2) and then annealed at 650.degree. C. for 3 hrs under a vacuum of
1.times.10.sup.-4 Torr for dehydrogenation and recrystallization, and as a
result, it was found that, according to the present invention, JIS grade 2
pure titanium having a fine equiaxed microstructure can be obtained.
EXAMPLE 7
An ingot of Ti-5Al-2.5Sn alloy as an .alpha. titanium alloy was heated in a
hydrogen atmosphere of 1 atmospheric pressure at 850.degree. C. for 1 to
24 hrs to prepare hydrogenated materials having hydrogen contents shown in
Table 20 and subjected to the .beta. heat treatment, i.e., heated at
1000.degree. C. for 2 hrs and then air-cooled to room temperature.
Thereafter, the materials were hot-rolled at each temperature shown in
Table 20 with a reduction of 40% to prepare 8 mm thick plates. After the
hot rolling, the plates were cooled to 500.degree. C., held for 8 hrs at
that temperature for aging. The aged plates were then annealed in vacuum
at 700.degree. C. for 10 hrs for dehydrogenation and recrystallization.
The microstructure of the central portion of each material was observed,
and as a result it was found that, as shown in Table 20, the plates
prepared by heating and hot-rolling materials having hydrogen contents of
0.20%, 1.4% and 2.2% by weight at 940.degree. C. and 1020.degree. C. in
the .beta. region, and then aging, had an intended fine equiaxed
microstructure. The materials having a hydrogen content as low as 0.007%
by weight did not provide an intended microstructure at any temperatures.
The microstructure of the materials having hydrogen contents of 0.20%,
1.4% and 2.2% by weight was refined to a certain extent by hot-rolling at
1120.degree. C., but an intended microstructure cannot be obtained from
these materials because the original .beta. grain in coarse. The material
having a hydrogen content of 2.2% by weight cracked during handling after
aging.
TABLE 20
______________________________________
Hydrogen
content
by weight
Hot rolling temp. (.degree.C.)
(%) 940 1020 1120
______________________________________
0.007 Coarse Coarse Coarse
equiaxed acicular acicular
microstructure
microstructure
microstructure
0.20 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
1.4 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
2.2 Fine equiaxed
Fine equiaxed
Partially coarse
microstructure
microstructure
acicular
microstructure
______________________________________
EXAMPLE 8
Welded construction materials prepared by allowing plates (thickness: 4 mm)
of Ti-6Al-4V alloy as an (.alpha.+.beta.) titanium alloy to be butt welded
were subjected to experiments with varied hydrogen contents and aging
temperatures (aging time: 8 hrs). All of the materials were annealed in
vacuum at 700.degree. C. for 5 hrs for dehydrogenation and
recrystallization.
The experimental conditions and evaluation results of microstructure of the
weld metal zone and heat affected zone of the finally obtained weld are
shown in Table 21. The material having a hydrogen content of 2.1% by
weight was very brittle after aging, and therefore, difficult to handle,
which made it impossible to conduct subsequent annealing. Thus, it is
apparent that, according to the present invention, materials having a fine
equiaxed microstructure can be obtained.
TABLE 21
______________________________________
Experimental conditions
Hydrogen
Aging
content by
temp. Evaluation results of microstructure
weight (%)
(.degree.C.)
Metal weld zone
Heat affected zone
______________________________________
0.01 500 Acicular Acicular
microstructure
microstructure
0.03 20 Fine equiaxed
Fine equiaxed
microstructure
microstructure
0.03 400 Fine equiaxed
Fine equiaxed
microstructure
microstructure
0.8 20 Fine equiaxed
Fine equiaxed
microstructure
microstructure
0.8 400 Fine equiaxed
Fine equiaxed
microstructure
microstructure
1.0 500 Fine equiaxed
Fine equiaxed
microstructure
microstructure
1.5 500 Fine equiaxed
Fine equiaxed
microstructure
microstructure
2.1 400 -- --
______________________________________
In the above-described Examples 1 and 2, experiments were conducted on
sheet materials, but the same effect was observed on materials having
various shapes, such as plate, bar and wire, cast materials and powder
compacts In the above-described Examples 3 to 7, experiments were
conducted on hot rolling of slabs and hot extrusion of ingots, but the
same effect was observed when billets and powder compacts were used as the
object material and when forging was used instead of the hot extrusion.
The present invention is not limited to the above-described Examples only.
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